XAdES (XML Advanced Electronic Signature)

XAdES applies an advanced electronic signature directly inside an XML document.

Definition

XAdES (XML Advanced Electronic Signature) is a set of extensions to the XML-DSig standard that turns a basic XML signature into an advanced electronic signature meeting regulatory requirements.

It standardises how the document itself carries the elements needed for legal validity: a reference to the signer's certificate, timestamps, a signature policy and revocation data.

How it works

XAdES defines several increasing levels of robustness:

• XAdES-B (baseline): signature plus essential attributes.
• XAdES-T: adds a timestamp proving the signing time.
• XAdES-LT / LTA: embeds certificates and revocation data for long-term validation, even after certificates expire.

The signature can be enveloped in the XML, enveloping, or detached.

Example

Spain's Facturae format requires a XAdES signature on every electronic invoice. Several continuous transaction controls (CTC) systems in Latin America — countries using a clearance model — likewise require a XAdES signature on the XML documents submitted to the tax authority.